Codebook design for beamformed CSI-RS for FD-MIMO

ABSTRACT

Codebook designs are disclosed for full-dimensional multiple-input-multiple output (FD-MIMO) wireless cellular systems. The FD-MIMO cookbooks employ channel state information reference signals (CSI-RS). The codebook designs are used in beamforming CSI-RSs by the enhanced nodeB (eNB), where the CSI-RS is sent to the user equipment (UE), enabling the UE to perform channel estimation. The codebooks support beam selection, co-phasing between polarizations, and beam combining.

CROSS-REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 U.S.C. § 371, this application is the United StatesNational Stage Application of International Patent Application No.PCT/IB2015/002620, filed on Dec. 24, 2015, claims priority to U.S.Provisional Patent Application No. 62/203,595, filed on Aug. 11, 2015,which is incorporated herein by reference in its entirely.

TECHNICAL FIELD

This application relates to channel state information reference signalsand their use in full-dimensional multiple-input-multiple-outputcellular networks.

BACKGROUND

The Evolved Packet Core (EPC) is the core network of advanced mobilecommunication systems. The EPC allows different radio accesstechnologies (RATs) to operate in an integrated manner. These radioaccess technologies include first generation wireless Local AreaNetworks (LANs), second generation (2G) systems, such as Global Systemfor Mobile communication, or GSM, third generation systems, such as theUniversal Mobile Telecommunication System (UMTS), and fourth generationsystems, such as Long Term Evolution (LTE).

Under LTE, a User Equipment (UE) connects to the EPC over the LTE accessnetwork known as E-UTRAN (short for Evolved UMTS Terrestrial RadioAccess Network) and communicates with a base station known as theEvolved NodeB (eNB). The EPC is a packet-switched network in which theInternet Protocol is used for all transport services. The EPC is part ofthe 3^(rd) Generation Partnership Project (3GPP) specification.

Multiple-input-multiple-output (MIMO) under LTE exploits multipleantennas at both the UE and the eNB to improve the robustness of datatransmissions (transmit diversity) and/or the data rate (spatialmultiplexing). Along with MIMO, beamforming is a technique used in LTEto improve signal transmission between the eNB and the UE. Instead ofbroadcasting a signal to a wide area, the eNB aims the signal toward theUE. One way to achieve this is by separating the signal to betransmitted into an array of separate antenna signals and then weightingthe magnitude and phase of each signal. An improvement of the receivedsignal under this technique is known as a beamforming gain.

Starting with Release 8 of the 3GPP specification, MIMO has beensupported and is found in many LTE cellular systems. However, asrecently as Releases 10 and 12, the MIMO enhancements were designed tosupport antenna configurations at the eNB that are capable of adaptationin the azimuth only.

Thus, there is desired a system design to overcome the shortcomings ofthe prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisdocument will become more readily appreciated as the same becomes betterunderstood by reference to the following detailed description, whentaken in conjunction with the accompanying drawings, wherein likereference numerals refer to like parts throughout the various views,unless otherwise specified.

FIG. 1 is a simplified diagram used to illustrate the codebook designmethod and apparatus for FD-MIMO, according to some embodiments;

FIG. 2 is a simplified illustration of a wireless cellular neighborhoodused to illustrate FD-MIMO, according to some embodiments;

FIG. 3 is a mapping of CSI reference signals for CSI configuration 0,normal cyclic prefix, which may be used by the codebook design methodand apparatus of FIG. 1, according to some embodiments;

FIG. 4 is a first codebook used by the codebook design method andapparatus of FIG. 1 for FD-MIMO cellular systems, according to someembodiments;

FIG. 5 is a second codebook used by the codebook design method andapparatus of FIG. 1 for FD-MIMO cellular systems, according to someembodiments;

FIG. 6 is a third codebook used by the codebook design method andapparatus of FIG. 1 for FD-MIMO cellular systems, according to someembodiments;

FIGS. 7A-7E are codebooks from the 3GPP specification, TS 36.211 v.11.4.0, section 5.3.3A.2 that are used to generate the third codebook ofFIG. 6, according to some embodiments;

FIG. 8 is a flow diagram illustrating operation of the codebook designmethod and apparatus of FIG. 1, according to some embodiments; and

FIG. 9 is a simplified block diagram of a UE capable of implementing thecodebook design method and apparatus of FIG. 1 using the codebooks ofFIGS. 4, 5, and 6, according to some embodiments.

DETAILED DESCRIPTION

In accordance with the embodiments described herein, codebook designsare disclosed for full-dimensional multiple-input-multiple output(FD-MIMO) wireless cellular systems. The FD-MIMO cookbooks employchannel state information reference signals (CSI-RS). The codebookdesigns are used in beamforming CSI-RSs by the enhanced Node-B (eNB) (socalled Class B), where the CSI-RS antenna ports are sent to the userequipment (UE) with the precoding (or beamforming) applied on themultiple antennas of the eNB, enabling the UE to perform estimation ofthe channel for CSI feedback after precoding (or beamforming). Thecodebooks for CSI support beam selection, co-phasing betweenpolarizations, and beam combining.

In the following detailed description, reference is made to theaccompanying drawings, which show by way of illustration specificembodiments in which the subject matter described herein may bepracticed. However, it is to be understood that other embodiments willbecome apparent to those of ordinary skill in the art upon reading thisdisclosure. In other instances, well-known structures, materials, oroperations are not shown or described in detail to avoid obscuringaspects of the disclosure. The following detailed description is,therefore, not to be construed in a limiting sense, as the scope of thesubject matter is defined by the claims.

One LTE Advanced (LTE-A) topic involves configurations having multipleantennas, at the eNB and/or the UE. To support the increased complexityof multi-antenna configurations, changes in both the types of referencesignals and feedback by the UE (channel estimation) are introduced inLTE-A.

Channel estimation is performed by the UE by measuring the transmissionchannel between the UE and the eNB. To do channel estimation, the UEreceives a reference signal, known to both the UE and the eNB, from theeNB. There are several different types of reference signals definedunder LTE. Cell-specific reference signals (CRS), for example, arelocated at each antenna port, and can be used by each UE in a cellserviced by the eNB. Antenna ports are logical entities and do notnecessarily correspond to a physical antenna. Introduced in LTE Release10, a channel state information reference signal (CSI-RS) isspecifically designed to enable the UE to do channel estimation inmulti-antenna configurations. CSI-RSs are transmitted less frequentlythan CRSs and each antenna port is associated with a different CSI-RS.

In performing channel estimation, the UE sends information, known aschannel state information (CSI), to the eNB. CSI consists of channelquality information (CQI), rank information (RI) and precoding matrixindication (PMI). CQI, for example, provides information about thesignal to noise plus interference ratio (SINR) of the transmissionchannel. Based on the CSI recommended by the UE, the eNB then applies anappropriate modulation and coding scheme (MCS) to subsequent UEtransmissions. A low SINR for one transmission channel may result in alow MCS being used relative to another transmission channel having ahigher (better) SINR. The eNB and the UE thereafter communicate usingthe MCS elected by the eNB, at least until the channel conditionsbetween them change.

The other components of the CSI, namely PMI and RI, are mainly relatedto the support of MIMO transmissions. As described above,multiple-input-multiple-output (MIMO) refers to multiple antennas oneither or both of the receiver or transmitter in a wireless cellularsystem. MIMO support commenced with Release 8 of the 3GPP specificationand is found in many LTE cellular systems.

Continuing with Releases 10 and 11 of the 3GPP specification, the MIMOenhancements continue to support antenna configurations that adapt thebeamforming in the azimuth direction only, with no reference to theadaptive beamforming in the elevation direction. The term “azimuth”describes the direction in the horizontal plane (e.g., parallel to theground) while the term “elevation” describes the direction in thevertical plane (e.g., orthogonal to the ground).

Previously under LTE, mainly linear antenna arrays were considered,which generally allowed beamforming in one dimension. Under LTE-A,antennas on two-dimensional antenna arrays are considered and, for this,the beamforming can be controlled in two dimensions. Such aconfiguration may be beneficial in, for example, suburban scenarios,where antennas are mounted below rooftops and atop very tall buildings.

Although the antennas remain in fixed positions, a technique known asadaptive beamforming may be used to control the beams transmitted fromthe antennas of the eNB. In adaptive beamforming, the signal or set ofsignals corresponding to multiple MIMO layers for transmission from theantenna array is pre-coded, or multiplied, by specific antenna weights.The precoding or beamforming weights may be arranged into a matrix whereeach row corresponds to the antenna ports and each column to the MIMOlayer. Depending on the selection of the weight, it is possible to skewor to change the beamforming from the antenna to the UE without changingthe physical antenna position.

The CSI or, more specifically, the PMI and RI received from the UE,enables the eNB to transmit the signal with an appropriate beam or beamsin case of multiple MIMO layers. The PMI and RI feedback from the UE tothe eNB are based on a codebook that facilitates adaptation of thebeamforming for subsequent Physical Downlink Shared CHannel (PDSCH) andPhysical Uplink Shared CHannel (PUSCH) transmissions, where PDSCH isused for downlink data transport and PUSCH is used for uplink datatransport. Populated with predetermined precoding vectors, the codebookis known to both the UE and the eNB.

The UE, based on the channel measurements taken on the CSI-RS, selectsappropriate precoding vectors that could maximize the data rate, theSINR, or other desired characteristics of the transmission channel.Although the eNB makes the final decision about how a signal is to beprecoded before transmission to the UE, the eNB receives a PMIrecommendation from the UE based on the UE channel measurements.

In MIMO, it is possible to transmit multiple beams (also known asspatial MIMO layers or MIMO layers) over the same time and frequencyresources to maximize spectral efficiency. The rank indicator (RI)indicates the number of MIMO layers that can be simultaneouslytransmitted to the UE. So, for example, if the UE is located within theline-of-sight to the base station, the base station can simultaneouslytransmit two signals over the same time and frequency resources byusing, for example, two orthogonal polarizations. Because of theirorthogonality, the two signals do not create interference with oneanother even though the same time and frequency resources are used.

Recently, there is an interest in enhancing system performance throughthe use of antenna systems having a two-dimensional array structure thatprovides adaptive control of the beams over both the elevation dimensionand the azimuth dimension. Known as full-dimensional (FD) MIMO, theadditional control over the elevation dimension enables a variety ofstrategies.

These strategies exploit the elevation dimension of the antenna forimproved performance between the UE and the eNB. Sector-specificelevation beamforming, for example, involves the adaptive control overthe vertical pattern beamwidth and/or downtilt. Vertical sectorization,also known as advanced sectorization in the vertical domain, can improveaverage system performance through the higher gain of the verticalsector patterns, but vertical sectorization generally does not involveadditional standardization support. User-specific (UE-specific)elevation beamforming promises to increase the signal tointerference-plus-noise ratio (SINR) statistics seen by the UEs bypointing the vertical antenna pattern in the direction of the UE. Insome embodiments, the UE-specific elevation beamforming causes lessinterference to adjacent sectors by steering the transmitted energy inelevation.

FIG. 1 is a simplified diagram used to illustrate a codebook designmethod and apparatus 500 for FD-MIMO, according to some embodiments. Theapparatus involved are a UE 50 and an eNB 40, downlink signals beingtransmitted from the eNB to the UE, an uplink signal being transmittedfrom the UE to the eNB, a selection of three different possiblecodebooks 100, 200, and 300, the CSI ports of CSI-RS (with 2*n of themin FIG. 1 denoted CSI-RS ports X₁,Y₁, X₂,Y₂, . . . , X_(n),Y_(n)) beingtransmitted in the downlink with different beamforming and polarization,and CSI being transmitted in the uplink. Based on the CSI-RS receivedfrom the eNB 40, the UE 50 takes one or more of the available codebooksto perform calculations that result in a CSI being transmitted to theeNB. The details of the codebook design method and apparatus 500 areprovided below.

FIG. 2 is a simplified illustration of a wireless cellular neighborhood80, used to illustrate two-dimensional beamforming, according to someembodiments. The wireless cellular neighborhood consists of an eNB 40and several UEs 50, with the UEs occupying a multiple-story building.The eNB 40 includes an antenna array 60 with 16 antennas, wherein60A-60H are a first set of antennas with one polarization and 61A-61Hare a second set of antennas of another polarization. The nearbymultiple-story building includes multiple UEs 50 being served by theeNB. The antenna array comprising antennas 60A-60H and 61A-61H aretransmitting beams 70A, 70B, and 70C of one polarization (dotted lines)and the same beams 71A, 71B, and 71C of another polarization (solidlines), to UEs 50A, 50B, and 50C, respectively.

Each beam 70A, 70B, 70C and 71A, 71B, 71C in FIG. 2 is being transmittedto a specific UE 50 in the wireless cellular neighborhood 80. Byemploying beamforming, the eNB is able to transmit the beamsdirectionally. A signal to be transmitted by an eNB having multipleantennas may be multiplied by different complex weights, using aprecoding vector, such that the signals transmitted by each antenna cantarget a specific location. The location may be a portion of thecellular region or a specific UE, with a goal being improved signaltransmission.

In FIG. 2, CSI-RS ports are not transmitted from the physical antennasof the eNB 40. Instead, the multiple antennas 60A-60H and 61A-61H makingup the antenna array 60 of the eNB are used to create one or more beams.Each CSI-RS antenna port (which is not a physical antenna) istransmitted in accordance to the beams of the eNB. In some embodiments,for each beam, two CSI-RS antenna ports are used, where each CSI-RS portcorresponds to the same beam, but different polarizations.

FIG. 3 is a mapping of CSI reference signals for CSI configuration 0,normal cyclic prefix (3GPP TS 36.211 version 10.0.0 Release 10, Section6.10.5.) The CSI reference signals may be used by the codebook designmethod and apparatus 500 of FIG. 1. Each CSI-RS antenna port istransmitted on a pair of resource element (REs) within a physicalresource block (PRB) pair, wherein a PRB in the case of a subframe witha normal cyclic prefix consists of twelve subcarriers in the vertical(frequency) direction and seven symbols in the horizontal (time)direction. The pair of CSI-RS ports transmitted on the same REs maycorrespond to the same beam or different beams. In this example, thepair of RE are used to transmit two CSI-RS ports with the samebeamforming and orthogonal polarizations, however the beam andpolarization assignment to antenna ports are not limited to thisexample.

The UE may be performing channel measurements on the CSI-RS antennaports. Using the codebook, the UE selects and evaluates differentcombinations of the selected CSI-RS antenna ports. The PDSCH and PUSCH,being the main downlink and uplink data-bearing channels, respectively,are subsequently transmitted on the favored combination.

During an FD-MIMO study item of the 3GPP specification, the support ofFD-MIMO by using beamformed CSI-RS resource scheme has been found as apromising approach. The scheme applies different beamforming to theCSI-RS antenna ports to achieve better coverage of the CSI-RStransmissions without increasing the maximum number of CSI-RS antennaports, as compared to the Release 12 LTE-A specification. Depending onthe beamforming design, however, the existing codebook structureavailable in Release 12 may not be applicable for the precoding overbeamformed CSI-RS antenna ports.

A codebook under LTE Release 8 supports up to four MIMO layers (rank 4).The codebook is characterized as having a constant modulus design, anested property, and employs minimal complex multiplications. Theconstant modulus property ensures that the power amplifier connected toeach antenna is loaded equally. The nested property is how the codebooksof different ranks are arranged such that a lower rank codebook is asubset of the higher rank codebook vectors, and ensures that the CQIcalculations are simplified across the different ranks. The minimalcomplex multiplications design rule is illustrated, for example, incodebook multiplications for two-antenna codebooks use +1, −1, +j, and−j, where j is an imaginary number.

Under LTE Release 10, a dual codebook for eight transmit antennas isintroduced. The dual codebook is a double four-bit codebook obtained bymultiplying two precoding matrices, denoted W₁ and W₂, where W₁represents long-term and wideband channel characteristics, and W₂represents short-term and subband channel characteristics. The LTERelease 10 dual codebook, also maintains the constant modulus propertyfor all codewords or PMI in the codebook.

The constant modulus property of the previous LTE codebooks may not beappropriate when CSI-RS antenna ports are differently beamformed, giventhat only part of the beams usually provides noticeable performanceimprovement at the UE. Therefore, the codebook design with non-constantmodulus property for the precoder is proposed as an enhancement to thebeamformed CSI-RS resources.

FIG. 4 (and equations (1)-(4) below) illustrate a first codebook 100used by the codebook design method and apparatus 500 to support FD-MIMOcellular systems, according to some embodiments. In contrast to priorart LTE codebooks, the codebook 100 does not exhibit a constant modulusproperty of the PMI elements. The codebook 100 does however support beamselection and co-phasing, as described in more detail below. Thecodebook 100 supports FD-MIMO systems with beamformed CSI-RS resources.

In some embodiments, for the beamformed CSI-RS approach where eachCSI-RS antenna port is differently beamformed, the codebook 100 followsthe structure of W₂ defined for Release 10 and Release 12 codebooks.More specifically, the codebook 100 supports beam-selection andco-phasing between polarizations. A second codebook 200, describedbelow, further supports the combining of different beams.

In some embodiments, the codebook 100 facilitates beam selection byintroducing a vector, e^(m), of length N_(p)/2, where N_(p) is the totalnumber of CSI-RS antenna ports. For the eNB antenna system withcross-polarized antenna elements, the N_(p)/2 may correspond to thenumber of beams configured for beam selection and co-phasing by theproposed codebook. The e^(m) vector is also known as a selection vector,with a value of “1” in the m^(th) position of the vector and a value of“0” in the other positions. The codebook 100 also features a complexscaling factor, e^(jα), for each beam selection vector. The complexscaling factor, e^(jα), provides the co-phasing of the beamscorresponding to the different polarizations. Co-phasing element, a,enables precoding across beams corresponding to different polarizations.In some embodiments, a, is either 0 or π/2.

Using the codebook 100, the transmission of multiple MIMO layers isprovided by using different polarizations over the same beam ordifferent beams. Then, assuming that the half of CSI-RS antenna portsN_(p)/2 corresponds to the beamformed antenna ports of the samepolarization, the codebook for rank 1-4 is defined as follows:

$\begin{matrix}{{{{Rank}\mspace{14mu} 1\left( {{one}\mspace{14mu}{MIMO}\mspace{14mu}{layer}} \right)}:}} & \; \\{{\frac{1}{\sqrt{2}}\begin{bmatrix}e^{m} \\{e^{j\;\alpha}e^{m}}\end{bmatrix}},} & \left( {1a} \right) \\{{\frac{1}{\sqrt{2}}\begin{bmatrix}e^{m} \\{{- e^{j\;\alpha}}e^{m}}\end{bmatrix}},{\left\{ m \right\} = 0},\ldots\mspace{14mu},{{N_{p}/2} - 1},{\left\{ \alpha \right\} = 0},{\pi/2}} & \left( {1b} \right)\end{matrix}$

where e^(m) is a selection vector of length N_(p)/2, where N_(p) is thetotal number of CSI-RS antenna ports. The e^(m) selection vector has avalue of “1” in the m^(th) position of the vector and a value of “0” inthe other positions. e^(jα) is the complex scaling factor and a is thepolarization (or co-phasing) element.

In equation (1a), it can be seen that the precoder for a single MIMOlayer is obtained by concatenation of two selection vectors e^(m). Thefirst selection vector, representing a selected beam m for the antennaports of one polarization and the second selection vector representing aselected beam m for the antennas of another polarization. In equation(1) the selection vector e^(m) is common for both the top and bottomelements of the rank 1 PMI, which corresponds to the selection of thesame beam m for the antennas of both polarizations. In equation (1) thebottom selection vector e^(m) is multiplied by the exponential term,e^(jα), that performs additional precoding of the signal transmitted bythe selected beam on the antennas of the second polarization.

The second set of the precoding vectors in equation (1b) also uses thesame selected beam m for both polarizations, and is only distinguishedfrom the first set of the precoding vectors by a minus iii the bottomvector to provide additional precoding of the signal transmitted by theselected beam on the antenna ports of the second polarization.

The e^(m) vector is useful because it indicates the appropriate beam forthe antenna ports of each polarizations and the precoding across thebeams of two polarizations for the data transmission. If there are eightantenna ports, the e^(m) vector will be a 4×1 selection vector, whichcorresponds to the four beams in case of antennas with twopolarizations. If there are four beams, then, depending on the precodingvector, when the UE is doing PMI feedback, by changing m, the UE willindicate one beam as preferred among the four possible measured beamsincluding the most appropriate precoding e^(jα) of the signals acrosstwo beams corresponding to two polarizations.

$\begin{matrix}{{{{Rank}\mspace{14mu} 2\left( {{two}\mspace{14mu}{MIMO}\mspace{14mu}{layers}} \right)}:}} & \; \\{{\frac{1}{\sqrt{4}}\begin{bmatrix}e^{m} & e^{m} \\{e^{j\;\alpha}e^{m}} & {{- e^{j\;\alpha}}e^{m}}\end{bmatrix}},{\left\{ m \right\} = 0},\ldots\mspace{14mu},{{N_{p}/2} - 1},{\left\{ \alpha \right\} = 0},{\pi/2}} & (2)\end{matrix}$

To support the nested property of the codebook 100, the rank 2 codebookentry has similar structure to the rank 1 entry. For the rank 2codebook, each PMI indicates the selected beam for two MIMO layers. Inequation (2) the precoding vector for two MIMO layers selects the samebeam m, but applies different precoding across the selected beam ofdifferent polarizations. The precoding for beams of differentpolarizations are selected to provide orthogonal polarizations for twoMIMO layers after precoding.

$\begin{matrix}{{{{Rank}\mspace{14mu} 3\left( {{three}\mspace{14mu}{MIMO}\mspace{14mu}{layers}} \right)}:}\mspace{425mu}} & \; \\{{\frac{1}{\sqrt{6}}\begin{bmatrix}e^{m} & e^{m} & e^{k} \\{e^{j\;\alpha}e^{m}} & {{- e^{j\;\alpha}}e^{m}} & {e^{j\;\beta}e^{k}}\end{bmatrix}},} & \left( {3a} \right) \\{{\frac{1}{\sqrt{6}}\begin{bmatrix}e^{m} & e^{k} & e^{k} \\{e^{j\;\alpha}e^{m}} & {e^{j\;\beta}e^{k}} & {{- e^{j\;\beta}}e^{k}}\end{bmatrix}},{\left\{ {m,k} \right\} = 0},\ldots\mspace{14mu},{{N_{p}/2} - 1},{m \neq k},{\left\{ {\alpha,\beta} \right\} = 0},{\pi/2}} & \left( {3b} \right)\end{matrix}$

where e^(k), like e^(m), is a selection vector of length N_(p)/2, whereN_(p) is the total number of CSI-RS antenna ports. The e^(k) vector hasa value of “1” in the k^(th) position of the vector and a value of “0”in the other positions, with k being different from m. Like the e^(jα)and e^(jβ) are also a complex scaling factors and β is the polarizationelement with α being the same as or different from β.

Under rank 3, for the first set of the PMIs (equation (3a)), the firsttwo MIMO layers are transmitted using the same beam m, given byselection vector e^(m) but using orthogonal polarizations achieve byusing orthogonal precoding across polarizations. The third columnhowever uses a second beam indicated by k which is different thanselected beam m and by using same or different co-phasing element, β.

For the second set of PMIs (equation (3b)), the first MIMO layer istransmitted using a first beam given by m, while the second and thirdMIMO layers are transmitted using the same second beam, given by k, thelatter two using orthogonal polarizations. The first MIMO layer uses theco-phasing element, α, and the second and third MIMO layers use theco-phasing element, β, where α and β may be the same or different.

$\begin{matrix}{{{{Rank}\mspace{14mu} 4\left( {{four}\mspace{14mu}{MIMO}\mspace{14mu}{layers}} \right)}:}\mspace{445mu}} & \; \\{{\frac{1}{\sqrt{8}}\begin{bmatrix}e^{m} & e^{m} & e^{k} & e^{k} \\{e^{j\;\alpha}e^{m}} & {{- e^{j\;\alpha}}e^{m}} & {e^{j\;\beta}e^{k}} & {{- e^{j\;\beta}}e^{k}}\end{bmatrix}},{\left\{ {m,k} \right\} = 0},\ldots\mspace{14mu},{{N_{p}/2} - 1},{m \neq k},{\left\{ {\alpha,\beta} \right\} = 0},{\pi/2}} & (4)\end{matrix}$

Under rank 4, two different MIMO layers, given by m and k, are used andtwo different polarizations determined by α and β are used. In the firstcolumn, the precoder for the first MIMO layer uses the beam, given by m.In the second column, the same beam m for the second MIMO layer is used,but with orthogonal polarization comparing to polarization of the firstbeam. In the third and fourth column, which determine precoding for thethird and fourth MIMO layer, the same beam k is used, which is differentfrom the selected beam m for the first MIMO layers. The polarizationsfor two MIMO layers determined by β are orthogonal for the third andfourth MIMO layers.

The codebook entries can be obtained by changing over all possiblecombinations of the parameters n, k, α, and β given by equations(1)-(4). Thus, the UE uses the codebook 100 to scan all possiblecombinations of the selected beams and co-phasing of polarization tofind the one (or more) with the best transmission characteristics. Insome embodiments, if the size of the codebook 100 for all possiblecombinations is large, the codebook size can be reduced by defining thecodebook, which uses subsets of all possible n, k, α, and β.

In some embodiments, the codebook 100 supports beam selection andco-phasing, as described above. Codebook designers of ordinary skill inthe art recognize that the entries (1)-(4) of the codebook 100 (and asillustrated in FIG. 4) may be adjusted without departing from theseprinciples.

FIG. 5 and equations (5)-(8) below illustrate a second codebook 200 usedby the codebook design method and apparatus 500, according to someembodiments. In the codebook 200, a d^(m,n) vector of length N_(p)/2 isnot an single beam selection vector, but instead includes a value of “1”in both the m^(th) and n^(th) positions (m≠n) of the vector, and a valueof “0” in the other positions. Thus, in addition to supporting singlebeam selection and co-phasing, the codebook 200 also supports two beamselection and combining. The codebook 200 is shown as follows:

$\begin{matrix}{{{{Rank}\mspace{14mu} 1\left( {{one}\mspace{14mu}{MIMO}\mspace{14mu}{layer}} \right)}:}} & \; \\{{\frac{1}{\sqrt{4}}\begin{bmatrix}d^{m,n} \\{e^{j\;\alpha}d^{m,n}}\end{bmatrix}},} & \left( {5a} \right) \\{{\frac{1}{\sqrt{4}}\begin{bmatrix}d^{m,n} \\{{- e^{j\;\alpha}}d^{m,n}}\end{bmatrix}},{\left\{ {m,n} \right\} = 0},\ldots\mspace{14mu},{{N_{p}/2} - 1},{m \neq n},{\left\{ \alpha \right\} = 0},{\pi/2}} & \left( {5b} \right)\end{matrix}$

where d^(m,n) is a vector of length N_(p)/2, where N_(p) is the totalnumber of CSI-RS antenna ports. The d^(m,n) vector has a value of “1” inthe m^(th) and n^(th) positions of the vector and a value of “0” in theother positions. The e^(jα) is the complex scaling factor and a is theco-phasing element.

$\begin{matrix}{{{{Rank}\mspace{14mu} 2\left( {{two}\mspace{14mu}{MIMO}\mspace{14mu}{layers}} \right)}:}} & \; \\{{\frac{1}{\sqrt{8}}\begin{bmatrix}d^{m,n} & d^{m,n} \\{e^{j\;\alpha}d^{m,n}} & {{- e^{j\;\alpha}}d^{m,n}}\end{bmatrix}},{\left\{ m \right\} = 0},\ldots\mspace{14mu},{{N_{p}/2} - 1},{\left\{ \alpha \right\} = 0},{\pi/2}} & (6)\end{matrix}$

To support nested property of the codebook 200, the rank 2 codebookstructure is similar to the rank 1 codebook structure. The precoding fortwo MIMO layers assumes the same selected beams for m and n for bothMIMO layers, but orthogonal polarizations determined by co-phasingelement a.

As in the codebook 100, the rank 3 entry for the codebook 200 includestwo different entries, given by equations (7a) and (7b), according tosome embodiments.

$\begin{matrix}{{{{Rank}\mspace{14mu} 3\left( {{three}\mspace{14mu}{MIMO}\mspace{14mu}{layers}} \right)}:}\mspace{425mu}} & \; \\{{\frac{1}{\sqrt{12}}\begin{bmatrix}d^{m,n} & d^{m,n} & d^{k,l} \\{e^{j\;\alpha}d^{m,n}} & {{- e^{j\;\alpha}}d^{m,n}} & {e^{j\;\beta}d^{k,l}}\end{bmatrix}},} & \left( {7a} \right) \\{{\frac{1}{\sqrt{12}}\begin{bmatrix}d^{m,n} & d^{k,l} & d^{k,l} \\{e^{j\;\alpha}d^{m,n}} & {e^{j\;\beta}d^{k,l}} & {{- e^{j\;\beta}}d^{k,l}}\end{bmatrix}},\left\{ {m,n} \right\},{\left\{ {k,l} \right\} = 0},\ldots\mspace{14mu},{{N_{p}/2} - 1},{m \neq n},{k \neq l},{\left\{ {\alpha,\beta} \right\} = 0},{\pi/2}} & \left( {7b} \right)\end{matrix}$

where, like d^(m,n), d^(k,l) is a vector of length N_(p)/2, where N_(p)is the total number of CSI-RS antenna ports. The d^(k,l) vector has avalue of “1” in the k^(th) and l^(th) positions of the vector and avalue of “0” in the other positions, with m being unequal to k. Thee^(jβ), is the complex scaling factor and β is the co-phasing element,with a being the same or different as β.

$\begin{matrix}{{{{Rank}\mspace{14mu} 4\left( {{four}\mspace{14mu}{MIMO}\mspace{14mu}{layers}} \right)}:}\mspace{445mu}} & \; \\{{\frac{1}{\sqrt{16}}\begin{bmatrix}d^{m,n} & d^{m,n} & d^{k,l} & d^{k,l} \\{e^{j\;\alpha}d^{m,n}} & {{- e^{j\;\alpha}}d^{m,n}} & {e^{j\;\beta}d^{k,l}} & {{- e^{j\;\beta}}d^{k,l}}\end{bmatrix}},\left\{ {m,n} \right\},{\left\{ {k,l} \right\} = 0},\ldots\mspace{14mu},{{N_{p}/2} - 1},{m \neq n},{k \neq l},{\left\{ {\alpha,\beta} \right\} = 0},{\pi/2}} & (8)\end{matrix}$

In another implementation of the codebook 200, the vector, d^(m,n), oflength N_(p)/2 includes a value of “1” in the m^(th) position and avalue of “−1” in the n^(th) positions (m≠n) and a value of “0” in theother positions.

In still another implementation of the codebook 200, the vector, d^(i),of length N_(p)/2 includes non-integer values in the m^(th) and n^(th)elements as follows:

$\begin{matrix}{d^{i} = \left\{ \begin{matrix}{d_{m},} & {i = m} \\{d_{n},} & {i = n} \\{0,} & {otherwise}\end{matrix} \right.} & (9)\end{matrix}$

where m≠n. This enables unequal power distribution between the twoselected beams. For example, d_(m)=√{square root over (0.8)},d_(n)=√{square root over (1.2)} such that, d_(m) ²+d_(n) ²=2.

Thus, in some embodiments, like the codebook 100, the codebook 200supports beam selection and co-phasing, as described above. Further, thecodebook 200 supports beam combining. Codebook designers of ordinaryskill in the art recognize that the entries (5)-(9) of the codebook 200(some of which is illustrated in FIG. 5) may be adjusted withoutdeparting from these principles.

As illustrated in FIG. 1, a third codebook 300 may be used by thecodebook design method and apparatus 500 to support FD-MIMO cellularsystems, according to some embodiments. The codebook 300 follows theuplink codebook defined in TS 36.211 v. 11.4.0, section 5.3.3A.2 tosupport uplink transmissions. Thus, as illustrated in FIG. 6, thecodebook 300 is made up of five different sets of codebooks from section5.3.3A.2. FIGS. 7A-7E illustrate the codebooks from which the codebook300 is generated.

FIG. 8 is a flow diagram illustrating the codebook design method 500 ofFIG. 1, according to some embodiments. The operations of the codebookdesign method 500 may take place in an order different than isillustrated.

The eNB transmits the CSI-RS signals comprising one or more CSI-RSantenna ports, where each CSI-RS antenna port corresponds to onebeamforming and one polarization (block 502). The eNB configures the UEwith CSI-RS signal parameters (e.g., number of CSI-RS antenna ports) forchannel measurements on CSI-RS antenna ports and the proposed codebookfor CSI calculation (block 504), for example, codebooks 100, 200, or300.

Having the CSI-RS signal parameters, the UE is able to performmeasurements on the CSI-RS antenna ports of the configured CSI-RS. TheUE scans over all possible PMIs of the configured codebook (block506-512). Once all possible PMIs have been used, the UE chooses the PMIthat provides the optimal performance (block 514). This enables the UEto report the CSI, including the selected PMI, the RI, and the CQI, tothe eNB (block 516). The eNB is thereafter able to transmit PDSCH to theUE, based on the received CSI from the UE, including beam(s) andco-phasing according to the selected PMI (block 518).

Thus, UE is able to choose the best PMI from the codebook (100, 200,300) every time it receives CSI-RS, which carries multiple CSI-RSantenna ports, where each CSI-RS port is differently beamformed orcorresponds to a different polarization.

As used herein, the term “circuitry” may refer to, be part of, orinclude an ASIC, an electronic circuit, a processor (shared, dedicated,or group), and/or memory (shared, dedicated, or group) that execute oneor more software or firmware programs, a combinational logic circuit,and/or other suitable hardware components that provide the describedfunctionality. In some embodiments, the circuitry may be implemented in,or functions associated with the circuitry may be implemented by, one ormore software or firmware modules. In some embodiments, circuitry mayinclude logic, at least partially operable in hardware.

Embodiments described herein may be implemented into a system using anysuitably configured hardware and/or software. FIG. 9 illustrates, forone embodiment, example components of a User Equipment (UE) device 800.In some embodiments, the UE device 800 may include application circuitry802, baseband circuitry 804, Radio Frequency (RF) circuitry 806,front-end module (FEM) circuitry 808 and one or more antennas 810,coupled together at least as shown.

The application circuitry 802 may include one or more applicationprocessors. For example, the application circuitry 802 may includecircuitry such as, but not limited to, one or more single-core ormulti-core processors. The processor(s) may include any combination ofgeneral-purpose processors and dedicated processors (e.g., graphicsprocessors, application processors, etc.). The processors may be coupledwith and/or may include a storage medium 812 or other type ofmemory/storage and may be configured to execute instructions stored inthe memory/storage to enable various applications and/or operatingsystems to run on the system.

The baseband circuitry 804 may include circuitry such as, but notlimited to, one or more single-core or multi-core processors. Thebaseband circuitry 804 may include one or more baseband processorsand/or control logic to process baseband signals received from a receivesignal path of the RF circuitry 806 and to generate baseband signals fora transmit signal path of the RF circuitry 806. Baseband processingcircuitry 804 may interface with the application circuitry 802 forgeneration and processing of the baseband signals and for controllingoperations of the RF circuitry 806. For example, in some embodiments,the baseband circuitry 804 may include a second generation (2G) basebandprocessor 804A, third generation (3G) baseband processor 804B, fourthgeneration (4G) baseband processor 804C, and/or other basebandprocessor(s) 804D for other existing generations, generations indevelopment, or to be developed in the future (e.g., fifth generation(5G), 6G, etc.). The baseband circuitry 804 (e.g., one or more ofbaseband processors 804A-D) may handle various radio control functionsthat enable communication with one or more radio networks via the RFcircuitry 806. The radio control functions may include, but are notlimited to, signal modulation/demodulation, encoding/decoding, radiofrequency shifting, etc. In some embodiments, modulation/demodulationcircuitry of the baseband circuitry 804 may include Fast-FourierTransform (FFT), precoding, and/or constellation mapping/demappingfunctionality. In some embodiments, encoding/decoding circuitry of thebaseband circuitry 804 may include convolution, tail-biting convolution,turbo, Viterbi, and/or Low Density Parity Check (LDPC) encoder/decoderfunctionality. Embodiments of modulation/demodulation andencoder/decoder functionality are not limited to these examples and mayinclude other suitable functionality in other embodiments.

In some embodiments, the baseband circuitry 804 may include elements ofa protocol stack such as, for example, elements of an EUTRAN protocolincluding, for example, physical (PHY), media access control (MAC),radio link control (RLC), packet data convergence protocol (PDCP),and/or radio resource control (RRC) elements. A central processing unit(CPU) 804E of the baseband circuitry 804 may be configured to runelements of the protocol stack for signaling of the PHY, MAC, RLC, PDCP,and/or RRC layers. In some embodiments, the baseband circuitry mayinclude one or more audio digital signal processor(s) (DSP) 804F. Theaudio DSP(s) 804F may include elements for compression/decompression andecho cancellation and may include other suitable processing elements inother embodiments. Components of the baseband circuitry may be suitablycombined in a single chip, a single chipset, or disposed on a samecircuit board in some embodiments. In some embodiments, some or all ofthe constituent components of the baseband circuitry 804 and theapplication circuitry 802 may be implemented together such as, forexample, on a system on a chip (SOC).

In some embodiments, the baseband circuitry 804 may provide forcommunication compatible with one or more radio technologies. Forexample, in some embodiments, the baseband circuitry 804 may supportcommunication with an EUTRAN and/or other wireless metropolitan areanetworks (WMAN), a wireless local area network (WLAN), or a wirelesspersonal area network (WPAN). Embodiments in which the basebandcircuitry 804 is configured to support radio communications of more thanone wireless protocol may be referred to as multi-mode basebandcircuitry.

RF circuitry 806 may enable communication with wireless networks usingmodulated electromagnetic radiation through a non-solid medium. Invarious embodiments, the RF circuitry 806 may include switches, filters,amplifiers, etc., to facilitate the communication with the wirelessnetwork. RF circuitry 806 may include a receive signal path which mayinclude circuitry to down-convert RF signals received from the FEMcircuitry 808 and provide baseband signals to the baseband circuitry804. RF circuitry 806 may also include a transmit signal path which mayinclude circuitry to up-convert baseband signals provided by thebaseband circuitry 804 and provide RF output signals to the FEMcircuitry 808 for transmission.

In some embodiments, the RF circuitry 806 may include a receive signalpath and a transmit signal path. The receive signal path of the RFcircuitry 806 may include mixer circuitry 806A, amplifier circuitry 806Band filter circuitry 806C. The transmit signal path of the RF circuitry806 may include filter circuitry 806C and mixer circuitry 806A. RFcircuitry 806 may also include synthesizer circuitry 806D forsynthesizing a frequency for use by the mixer circuitry 806A of thereceive signal path and the transmit signal path. In some embodiments,the mixer circuitry 806A of the receive signal path may be configured todown-convert RF signals received from the FEM circuitry 808 based on thesynthesized frequency provided by synthesizer circuitry 806D. Theamplifier circuitry 806B may be configured to amplify the down-convertedsignals and the filter circuitry 806C may be a low-pass filter (LPF) orband-pass filter (BPF) configured to remove unwanted signals from thedown-converted signals to generate output baseband signals. Outputbaseband signals may be provided to the baseband circuitry 804 forfurther processing. In some embodiments, the output baseband signals maybe zero-frequency baseband signals, although this is not a requirement.In some embodiments, mixer circuitry 806A of the receive signal path maycomprise passive mixers, although the scope of the embodiments is notlimited in this respect.

In some embodiments, the mixer circuitry 806A of the transmit signalpath may be configured to up-convert input baseband signals based on thesynthesized frequency provided by the synthesizer circuitry 806D togenerate RF output signals for the FEM circuitry 808. The basebandsignals may be provided by the baseband circuitry 804 and may befiltered by filter circuitry 806C. The filter circuitry 806C may includea low-pass filter (LPF), although the scope of the embodiments is notlimited in this respect.

In some embodiments, the mixer circuitry 806A of the receive signal pathand the mixer circuitry 806A of the transmit signal path may include twoor more mixers and may be arranged for quadrature down-conversion and/orup-conversion, respectively. In some embodiments, the mixer circuitry806A of the receive signal path and the mixer circuitry 806A of thetransmit signal path may include two or more mixers and may be arrangedfor image rejection (e.g., Hartley image rejection). In someembodiments, the mixer circuitry 806A of the receive signal path and themixer circuitry may be arranged for direct down-conversion and/or directup-conversion, respectively. In some embodiments, the mixer circuitry806A of the receive signal path and the mixer circuitry of the transmitsignal path may be configured for super-heterodyne operation.

In some embodiments, the output baseband signals and the input basebandsignals may be analog baseband signals, although the scope of theembodiments is not limited in this respect. In some alternateembodiments, the output baseband signals and the input baseband signalsmay be digital baseband signals. In these alternate embodiments, the RFcircuitry 806 may include analog-to-digital converter (ADC) anddigital-to-analog converter (DAC) circuitry and the baseband circuitry804 may include a digital baseband interface to communicate with the RFcircuitry 806.

In some dual-mode embodiments, a separate radio IC circuitry may beprovided for processing signals for each spectrum, although the scope ofthe embodiments is not limited in this respect.

In some embodiments, the synthesizer circuitry 806D may be afractional-N synthesizer or a fractional N/N+1 synthesizer, although thescope of the embodiments is not limited in this respect as other typesof frequency synthesizers may be suitable. For example, synthesizercircuitry 806D may be a delta-sigma synthesizer, a frequency multiplier,or a synthesizer comprising a phase-locked loop with a frequencydivider.

The synthesizer circuitry 806D may be configured to synthesize an outputfrequency for use by the mixer circuitry 806A of the RF circuitry 806based on a frequency input and a divider control input. In someembodiments, the synthesizer circuitry 806D may be a fractional N/N+1synthesizer.

In some embodiments, frequency input may be provided by a voltagecontrolled oscillator (VCO), although that is not a requirement. Dividercontrol input may be provided by either the baseband circuitry 804 orthe applications processor 802, depending on the desired outputfrequency. In some embodiments, a divider control input (e.g., N) may bedetermined from a look-up table based on a channel indicated by theapplications processor 802.

Synthesizer circuitry 806D of the RF circuitry 806 may include adivider, a delay-locked loop (DLL), a multiplexer, and a phaseaccumulator. In some embodiments, the divider may be a dual modulusdivider (DMD) and the phase accumulator may be a digital phaseaccumulator (DPA). In some embodiments, the DMD may be configured todivide the input signal by either N or N+1 (e.g., based on a carry out)to provide a fractional division ratio. In some example embodiments, theDLL may include a set of cascaded, tunable, delay elements, a phasedetector, a charge pump, and a D-type flip-flop. In these embodiments,the delay elements may be configured to break a VCO period up into N_(d)equal packets of phase, where N_(d) is the number of delay elements inthe delay line. In this way, the DLL provides negative feedback to helpensure that the total delay through the delay line is one VCO cycle.

In some embodiments, synthesizer circuitry 806D may be configured togenerate a carrier frequency as the output frequency, while in otherembodiments, the output frequency may be a multiple of the carrierfrequency (e.g., twice the carrier frequency, four times the carrierfrequency), and used in conjunction with quadrature generator anddivider circuitry to generate multiple signals at the carrier frequencywith multiple different phases with respect to each other. In someembodiments, the output frequency may be a LO frequency (f_(LO)). Insome embodiments, the RF circuitry 806 may include an IQ/polarconverter.

FEM circuitry 808 may include a receive signal path which may includecircuitry configured to operate on RF signals received from one or moreantennas 810, amplify the received signals and provide the amplifiedversions of the received signals to the RF circuitry 806 for furtherprocessing. FEM circuitry 808 may also include a transmit signal pathwhich may include circuitry configured to amplify signals fortransmission provided by the RF circuitry 806 for transmission by one ormore of the one or more antennas 810.

In some embodiments, the FEM circuitry 808 may include a TX/RX switch toswitch between transmit mode and receive mode operation. The FEMcircuitry may include a receive signal path and a transmit signal path.The receive signal path of the FEM circuitry may include a low-noiseamplifier (LNA) to amplify received RF signals and provide the amplifiedreceived RF signals as an output (e.g., to the RF circuitry 806). Thetransmit signal path of the FEM circuitry 808 may include a poweramplifier (PA) to amplify input RF signals (e.g., provided by RFcircuitry 806), and one or more filters to generate RF signals forsubsequent transmission (e.g., by one or more of the one or moreantennas 810.

In some embodiments, the UE device 800 may include additional elementssuch as, for example, memory/storage, display, camera, sensor, and/orinput/output (I/O) interface.

Various techniques, or certain aspects or portions thereof, may take theform of program code (i.e., instructions) embodied in tangible media,such as floppy diskettes, CD-ROMs, hard drives, non-transitory computerreadable storage medium, or any other machine-readable storage mediumwherein, when the program code is loaded into and executed by a machine,such as a computer, the machine becomes an apparatus for practicing thevarious techniques. A non-transitory computer-readable storage mediumcan be a computer-readable storage medium that does not include asignal. In the case of program code execution on programmable computers,the computing device may include a processor, a storage medium readableby the processor (including volatile and non-volatile memory and/orstorage elements), at least one input device, and at least one outputdevice. The volatile and non-volatile memory and/or storage elements maybe a RAM, EPROM, flash drive, optical drive, magnetic hard drive,solid-state drive, or other medium for storing electronic data. The nodeand wireless device may also include a transceiver module, a computermodule, a processing module, and/or a clock module or timer module. Oneor more programs that may implement or utilize the various techniquesdescribed herein may use an application programming interface (API),reusable controls, and the like. Such programs may be implemented in ahigh-level procedure or object-oriented programming language tocommunicate with a computer system. However, the program(s) may beimplemented in assembly or machine language, if desired. In any case,the language may be a compiled or interpreted language, and combinedwith hardware implementations.

It should be understood that many of the functional units described inthe specification have been labeled as modules, in order to moreparticularly emphasize their implementation independence. For example, amodule may be implemented as a hardware circuit comprising custom VLSIcircuits or gate arrays, off-the-shelf semiconductors such as logicchips, transistors, or other discrete components. A module may also beimplemented in programmable hardware devices such as field programmablegate arrays, programmable array logic, programmable logic devices, orthe like.

Modules may also be implemented in software for execution by varioustypes of processors. An identified module of executable code may, forinstance, comprise one or more physical or logical blocks of computerinstructions, which may, for instance, be organized as an object,procedure, or function. Nevertheless, the executables of an identifiedmodule may be not physically located together, but may comprisedisparate instructions stored in different locations which, when joinedlogically together, comprise the module and achieve the stated purposefor the module.

Indeed, a module of executable code may be a single instruction, or manyinstructions, and may even be distributed over several different codesegments, among different programs, and across several memory devices.Similarly, operational data may be identified and illustrated hereinwithin modules, and may be embodied in any suitable form and organizedwithin any suitable type of data structure. The operational data may becollected as a single data set, or may be distributed over differentlocations including over different storage devices, and may exist, atleast partially, merely as electronic signals on a system or network.The modules may be passive or active, including agents operable toperform desired functions.

Reference throughout this specification to “an example” or means that aparticular feature, structure, or characteristic described in connectionwith the example is included in at least one embodiment. Thus,appearances of the phrases, “in an example” or “in some embodiments” invarious places throughout this specification are not necessarily allreferring to the same embodiment.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary. In addition, various embodiments and examples may be referredto herein along with alternatives for the various components thereof. Itis understood that such embodiments, examples, and alternatives are notto be construed as de facto equivalents of one another, but are to beconsidered as separate and autonomous representations. Furthermore, thedescribed features, structures, or characteristics may be combined inany suitable manner in one or more embodiments.

In summary, the codebook design method and apparatus 500 can beimplemented, in a first example, as part of a user equipment (UE) toperform channel estimation of a transmission channel of a wirelesscellular network, where the UE measures a channel state informationreference signal (CSI-RS) of a downlink signal received on thetransmission channel, calculates channel state information (CSI) of thetransmission channel using a codebook along with the CSI-RS, thecodebook comprising a plurality of precoding matrices, the codebookfurther comprising non-constant modulus elements with at least twonon-zero elements in each precoding vector; and reports the CSI of thetransmission channel by way of an uplink transmission.

Further to the first example or any other example discussed herein, in asecond example, the UE calculates the CSI of the transmission channelusing a precoding matrix of the codebook, wherein each vector of theprecoding matrix comprises a concatenation at least two selectionvectors and each selection vector comprises a single non-zero elementand remaining zero elements.

Further to the second example or any other example discussed herein, ina third example, the UE calculates the CSI of the transmission channelusing the precoding matrix of the codebook, wherein the non-zero elementin the selection vector has a first amplitude and a first phase and thesecond non-zero element has the first amplitude and a second phase,wherein the first phase differs from the second phase by 0, π/2, 2π/2,or 3π/2.

Further to the first example or any other example discussed herein, in afourth example, the UE calculate the CSI of the transmission channelusing a precoding matrix of the codebook, wherein each vector of theprecoding matrix comprises a concatenation of at least two selectionvectors and each selection vector comprises a first non-zero element, asecond non-zero element, and the remaining zero elements.

Further to the fourth example or any other example discussed herein, ina fifth example, the first and second non-zero element in the firstselection vector has a first amplitude and the first and second non-zeroelement in the second selection vector has a second amplitude and asecond phase, wherein the first phase differs from the second phase by0, π/2, π, or 3π/4.

Further to the fourth example or any other example discussed herein, ina sixth example, the first non-zero element in the selection vector hasa first amplitude and a first phase and the second non-zero element hasthe first amplitude and a second phase, wherein the first phase differsfrom the second phase by 0 or π.

Further to the first example or any other example discussed herein, in aseventh example, the UE calculates the CSI of the transmission channelusing the codebook, wherein each of the plurality of matrices in thecodebook comprises vectors in which each vector comprises four non-zeroelements and remaining zero elements.

Further to the fourth example or any other example discussed herein, inan eighth example, the first non-zero element has a first amplitude anda first phase and the second non-zero element has the first amplitudeand a second phase, wherein the first phase differs from the secondphase by 0, π/2, π, or 3π/2.

Further to the first example or any other example discussed herein, in aninth example, the UE calculates the CSI of the transmission channelusing the codebook, wherein the codebook for rank 1 CSI reportingcontains at least one element from the following set of the vectors:

${\frac{1}{\sqrt{2}}\begin{bmatrix}e^{m} \\{e^{j\;\alpha}e^{m}}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}e^{m} \\{{- e^{j\;\alpha}}e^{m}}\end{bmatrix}},{\left\{ m \right\} = 0},\ldots\mspace{14mu},{{N_{p}/2} - 1},{\left\{ \alpha \right\} = 0},{\pi/2},$

wherein e^(m) is a selection vector of length N_(p)/2, N_(p) is a totalnumber of CSI-RS antenna ports.

Further to the first example or any other example discussed herein, in atenth example, the UE calculates the CSI of the transmission channelusing the codebook, wherein the codebook for rank 2 CSI reportingcontains at least one element from the following set:

${\frac{1}{\sqrt{4}}\begin{bmatrix}e^{m} & e^{m} \\{e^{j\;\alpha}e^{m}} & {{- e^{j\;\alpha}}e^{m}}\end{bmatrix}},{\left\{ m \right\} = 0},\ldots\mspace{14mu},{{N_{p}/2} - 1},{\left\{ \alpha \right\} = 0},{\pi/2},$

wherein e^(m) is a selection vector of length N_(p)/2, N_(p) is a totalnumber of CSI-RS antenna ports.

Further to the first example or any other example discussed herein, inan eleventh example, the UE calculates the CSI of the transmissionchannel using the codebook, wherein the codebook for rank 3 CSIreporting contains at least one element from the following set:

${\frac{1}{\sqrt{6}}\begin{bmatrix}e^{m} & e^{m} & e^{k} \\{e^{j\;\alpha}e^{m}} & {{- e^{j\;\alpha}}e^{m}} & {e^{j\;\beta}e^{k}}\end{bmatrix}},{\frac{1}{\sqrt{6}}\begin{bmatrix}e^{m} & e^{k} & e^{k} \\{e^{j\;\alpha}e^{m}} & {e^{j\;\beta}e^{k}} & {{- e^{j\;\beta}}e^{k}}\end{bmatrix}},{\left\{ {m,k} \right\} = 0},\ldots\mspace{14mu},{{N_{p}/2} - 1},{m \neq k},{\left\{ {\alpha,\beta} \right\} = 0},{\pi/2}$

wherein e^(m) is a selection vector of length N_(p)/2, N_(p) is a totalnumber of CSI-RS antenna ports.

Further to the first example or any other example discussed herein, in atwelfth example, the UE calculate the CSI of the transmission channelusing the codebook, wherein the codebook for rank 4 CSI reportingcontains at least one element from the following set:

${\frac{1}{\sqrt{8}}\begin{bmatrix}e^{m} & e^{m} & e^{k} & e^{k} \\{e^{j\;\alpha}e^{m}} & {{- e^{j\;\alpha}}e^{m}} & {e^{j\;\beta}e^{k}} & {{- e^{j\;\beta}}e^{k}}\end{bmatrix}},{\left\{ {m,k} \right\} = 0},\ldots\mspace{14mu},{{N_{p}/2} - 1},{m \neq k},{\left\{ {\alpha,\beta} \right\} = 0},{\pi/2}$

wherein e^(m) is a selection vector of length N_(p)/2, N_(p) is thetotal number of CSI-RS antenna ports.

Further to any one of the ninth through the twelfth examples or anyother example discussed herein, in a thirteenth example, a value of “1”occupies an m^(th) position of the vector and a value of “0” occupiesother positions of the vector.

Further to the fourth example or any other example discussed herein, ina fifteenth example, the UE calculates the CSI of the transmissionchannel using the codebook, wherein the codebook for rank 2 CSIreporting contains at least one element from the following set:

${\frac{1}{\sqrt{8}}\begin{bmatrix}d^{m,n} & d^{m,n} \\{e^{j\;\alpha}d^{m,n}} & {{- e^{j\;\alpha}}d^{m,n}}\end{bmatrix}},{\left\{ m \right\} = 0},\ldots\mspace{14mu},{{N_{p}/2} - 1},{\left\{ \alpha \right\} = 0},{\pi/2},$

wherein d^(m,n) is a vector of length N_(p)/2.

Further to the fourth example or any other example discussed herein, ina sixteenth example, the UE calculates the CSI of the transmissionchannel using the codebook, wherein the codebook for rank 3 CSIreporting contains at least one element from the following set:

$\frac{1}{\sqrt{12}}\begin{bmatrix}d^{m,n} & d^{m,n} & d^{k,l} \\{e^{j\;\alpha}d^{m,n}} & {{- e^{j\;\alpha}}d^{m,n}} & {e^{j\;\beta}d^{k,l}}\end{bmatrix}$ ${\frac{1}{\sqrt{12}}\begin{bmatrix}d^{m,n} & d^{k,l} & d^{k,l} \\{e^{j\;\alpha}d^{m,n}} & {e^{j\;\beta}d^{k,l}} & {{- e^{j\;\beta}}d^{k,l}}\end{bmatrix}},\left\{ {m,n} \right\},{\left\{ {k,l} \right\} = 0},\ldots\mspace{14mu},{{N_{p}/2} - 1},{m \neq n},{k \neq l},{\left\{ {\alpha,\beta} \right\} = 0},{\pi/2}$

wherein d^(m,n) is a vector of length N_(p)/2.

Further to the fourth example or any other example discussed herein, ina seventeenth example, the UE calculates the CSI of the transmissionchannel using the codebook, wherein the codebook for rank 4 CSIreporting contains at least one element from the following set:

${\frac{1}{\sqrt{16}}\begin{bmatrix}d^{m,n} & d^{m,n} & d^{k,l} & d^{k,l} \\{e^{j\;\alpha}d^{m,n}} & {{- e^{j\;\alpha}}d^{m,n}} & {e^{j\;\beta}d^{k,l}} & {{- e^{j\;\beta}}d^{k,l}}\end{bmatrix}},\left\{ {m,n} \right\},{\left\{ {k,l} \right\} = 0},\ldots\mspace{14mu},{{N_{p}/2} - 1},{m \neq n},{k \neq l},{\left\{ {\alpha,\beta} \right\} = 0},{\pi/2}$

wherein d^(m,n) is a vector of length N_(p)/2

Further to any one of the fourteenth through the seventeenth examples orany other example discussed herein, in a eighteenth example, in vectord^(m,n) a value of “1” occupies an m^(th) position of the vector, avalue of “−1” occupies an n^(th) position of the vector, where m isunequal to n, and a value of “0” occupies other positions of the vector.

Further to any one of the fourteenth through the seventeenth examples orany other example discussed herein, in a nineteenth example, in vectord^(m,n), a value of “1” occupies the m^(th) and n^(th) positions of thevector, where m is unequal to n, and a value of “0” occupies the otherpositions of the vector, or a value of “1” occupies the m^(th) position,a value of “−1” occupies the n^(th) positions of the vector, and a valueof “0” occupies other positions of the vector.

Further to any one of the fourteenth through the seventeenth examples orany other example discussed herein, in a twentieth example, in vectord^(m,n) a non-integer value occupies the m^(th) and n^(th) positions,where m is unequal to n, and a value of “0” occupies the otherpositions.

Further to any one of the fourteenth through the seventeenth examples orany other example discussed herein, in a twenty-first example, thevector, d^(m,n), of length N_(p)/2 includes non-integer values in then^(th) and m^(th) elements (noted as d^(i)), where m us unequal to n, asfollows:

$d^{i} = \left\{ \begin{matrix}{d_{m},} & {i = m} \\{d_{n},} & {i = n} \\{0,} & {otherwise}\end{matrix} \right.$

wherein m is not equal to n.

Further to the first example or any other example discussed herein, in atwenty-second example, the codebook follows an uplink codebook definedin TS 36.211 v. 11.4.0, section 5.3.3A.2 to support uplinktransmissions.

Further, the codebook design method and apparatus 500 can beimplemented, in a twenty-third example, by an apparatus to operate in acellular network, the apparatus comprising a plurality of antennas toreceive and transmit signals, a codebook comprising a matrix, the matrixcomprising non-constant modulus elements, wherein each column of thematrix corresponds to a multiple-input-multiple-output (MIMO) layer andeach row of the matrix corresponds to an antenna port and wherein eachprecoding vector contains at least two non-zero elements, and basebandcircuitry to receive a radio frame comprising a channel stateinformation reference signal (CSI-RS), calculate channel stateinformation (CSI) using both the CSI-RS and the codebook, and report theCSI to the cellular network.

Further to the twenty-third example or any other example discussedherein, in a twenty-fourth example, the codebook comprises a firstcodebook comprising precoding matrices for rank 1, rank 2, rank 3, andrank 4, the first codebook comprising first selection vectors of lengthN_(p)/2, where N_(p) is a total number of CSI-RS antenna ports, whereina value of “1” occupies an m^(th) position and a value of “0” occupiesother positions of the first selection vectors, and a second codebookalso comprising precoding matrices for rank 1, rank 2, rank 3, and rank4, the second codebook comprising second selection vectors of lengthN_(p)/2, wherein a value of “1” occupies the m^(th) and n^(th) positionsof the second selection vectors, where m is unequal to n, and a value of“0” occupies the other positions of the second selection vectors, or avalue of “1” occupies the m^(th) position, a value of “−1” occupies then^(th) positions of the second selection vectors, and a value of “0”occupies other positions of the second selection vectors.

Further, the codebook design method and apparatus 500 can beimplemented, in a twenty-fifth example, by machine-readable storageincluding machine-readable instructions, when executed, to realize anapparatus as claimed in any preceding example.

While the foregoing examples are illustrative of the principles in oneor more particular applications, it will be apparent to those ofordinary skill in the art that numerous modifications in form, usage,and details of implementation can be made without the exercise ofinventive faculty, and without departing from the principles andconcepts herein and will appreciate numerous modifications andvariations therefrom. It is intended that the appended claims cover allsuch modifications and variations as fall within the true spirit andscope of the disclosed embodiments.

We claim:
 1. A user equipment (UE) to perform channel estimation of atransmission channel of a wireless cellular network, the UE isconfigured to: measure a channel state information reference signal(CSI-RS) of a downlink signal received on the transmission channel;calculate channel state information (CSI) of the transmission channelusing a codebook along with the CSI-RS, the codebook comprising aplurality of precoding matrices, the codebook further comprisingnon-constant modulus elements with at least two non-zero elements in aprecoding vector among a plurality of vectors of the codebook; andreport the CSI of the transmission channel by way of an uplinktransmission.
 2. The UE of claim 1, the UE to further: calculate the CSIof the transmission channel using a precoding matrix of the codebook,wherein each vector of the precoding matrix comprises a concatenation atleast two selection vectors and each selection vector comprises a singlenon-zero element and remaining zero elements.
 3. The UE of claim 2, theUE to further: calculate the CSI of the transmission channel using theprecoding matrix of the codebook, wherein the single non-zero element inthe selection vector has a first amplitude and a first phase and asecond non-zero element has the first amplitude and a second phase,wherein the first phase differs from the second phase by 0, π/2, 2π/2,or 3π/2.
 4. The UE of claim 1, the UE to further: calculate the CSI ofthe transmission channel using a precoding matrix of the codebook,wherein each vector of the precoding matrix comprises a concatenation ofat least two selection vectors and each selection vector comprises afirst non-zero element, a second non-zero element, and remaining zeroelements.
 5. The UE of claim 4, wherein the first and second non-zeroelement in a first selection vector has a first amplitude and the firstand second non-zero element in a second selection vector has a secondamplitude and a second phase, wherein a first phase differs from thesecond phase by 0, π/2, π, or 3π/4.
 6. The UE of claim 4, wherein thefirst non-zero element in the selection vector has a first amplitude anda first phase and the second non-zero element has the first amplitudeand a second phase, wherein the first phase differs from the secondphase by 0 or π.
 7. The UE of claim 1, the UE to further: calculate theCSI of the transmission channel using the codebook, wherein each of theplurality of matrices in the codebook comprises vectors in which eachvector comprises four non-zero elements and remaining zero elements. 8.The UE of claim 4, wherein the first non-zero element has a firstamplitude and a first phase and the second non-zero element has thefirst amplitude and a second phase, wherein the first phase differs fromthe second phase by 0, π/2, π, or 3π/2.
 9. The UE of claim 1, the UE tofurther: calculate the CSI of the transmission channel using thecodebook, wherein the codebook for rank 1 CSI reporting contains atleast one element from the following set of the vectors:${\frac{1}{\sqrt{2}}\begin{bmatrix}e^{m} \\{e^{j\;\alpha}e^{m}}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}e^{m} \\{{- e^{j\;\alpha}}e^{m}}\end{bmatrix}},{\left\{ m \right\} = 0},\ldots\mspace{14mu},{{N_{p}/2} - 1},{\left\{ \alpha \right\} = 0},{\pi/2},$wherein e^(m) is a selection vector of length N_(p)/2, N_(p) is a totalnumber of CSI-RS antenna ports.
 10. The UE of claim 1, the UE tofurther: calculate the CSI of the transmission channel using thecodebook, wherein the codebook for rank 2 CSI reporting contains atleast one element from the following set:${\frac{1}{\sqrt{4}}\begin{bmatrix}e^{m} & e^{m} \\{e^{j\;\alpha}e^{m}} & {{- e^{j\;\alpha}}e^{m}}\end{bmatrix}},{\left\{ m \right\} = 0},\ldots\mspace{14mu},{{N_{p}/2} - 1},{\left\{ \alpha \right\} = 0},{\pi/2},$wherein e^(m) is a selection vector of length N_(p)/2, N_(p) is a totalnumber of CSI-RS antenna ports.
 11. The UE of claim 1, the UE tofurther: calculate the CSI of the transmission channel using thecodebook, wherein the codebook for rank 3 CSI reporting contains atleast one element from the following set:${\frac{1}{\sqrt{16}}\begin{bmatrix}e^{m} & e^{m} & e^{k} \\{e^{j\;\alpha}e^{m}} & {{- e^{j\;\alpha}}e^{m}} & {e^{j\;\beta}e^{k}}\end{bmatrix}},{\frac{1}{\sqrt{16}}\begin{bmatrix}e^{m} & e^{k} & e^{k} \\{e^{j\;\alpha}e^{m}} & {e^{j\;\beta}e^{k}} & {{- e^{j\;\beta}}e^{k}}\end{bmatrix}},{\left\{ {m,k} \right\} = 0},\ldots\mspace{14mu},{{N_{p}/2} - 1},{m \neq k},{\left\{ {\alpha,\beta} \right\} = 0},{\pi/2}$wherein e^(m) is a selection vector of length N_(p)/2, N_(p) is a totalnumber of CSI-RS antenna ports.
 12. The UE of claim 1, the UE tofurther: calculate the CSI of the transmission channel using thecodebook, wherein the codebook for rank 4 CSI reporting contains atleast one element from the following set:${\frac{1}{\sqrt{8}}\begin{bmatrix}e^{m} & e^{m} & e^{k} & e^{k} \\{e^{j\;\alpha}e^{m}} & {{- e^{j\;\alpha}}e^{m}} & {e^{j\;\beta}e^{k}} & {{- e^{j\;\beta}}e^{k}}\end{bmatrix}},{\left\{ {m,k} \right\} = 0},\ldots\mspace{14mu},{{N_{p}/2} - 1},{m \neq k},{\left\{ {\alpha,\beta} \right\} = 0},{\pi/2}$wherein e^(m) is a selection vector of length N_(p)/2, N_(p) is a totalnumber of CSI-RS antenna ports.
 13. The UE of claim 9, wherein a valueof “1” occupies an m^(th) position of the vector and a value of “0”occupies other positions of the vector.
 14. The UE of claim 4, the UE tofurther: calculate the CSI of the transmission channel using thecodebook, wherein the codebook for rank 1 CSI reporting contains atleast one element from the following set:${\frac{1}{\sqrt{4}}\begin{bmatrix}d^{m,n} \\{e^{j\;\alpha}d^{m,n}}\end{bmatrix}},{\frac{1}{\sqrt{4}}\begin{bmatrix}d^{m,n} \\{{- e^{j\;\alpha}}d^{m,n}}\end{bmatrix}},{\left\{ {m,n} \right\} = 0},\ldots\mspace{14mu},{{N_{p}/2} - 1},{m \neq n},{\left\{ \alpha \right\} = 0},{\pi/2}$wherein d^(m,n) is a vector of length N_(p)/2.
 15. The UE of claim 4,the UE to further: calculate the CSI of the transmission channel usingthe codebook, wherein the codebook for rank 2 CSI reporting contains atleast one element from the following set:${\frac{1}{\sqrt{8}}\begin{bmatrix}d^{m,n} & d^{m,n} \\{e^{j\;\alpha}d^{m,n}} & {{- e^{j\;\alpha}}d^{m,n}}\end{bmatrix}},{\left\{ m \right\} = 0},\ldots\mspace{14mu},{{N_{p}/2} - 1},{\left\{ \alpha \right\} = 0},{\pi/2},$wherein d^(m,n) is a vector of length N_(p)/2.
 16. The UE of claim 4,the UE to further: calculate the CSI of the transmission channel usingthe codebook, wherein the codebook for rank 3 CSI reporting contains atleast one element from the following set:$\frac{1}{\sqrt{12}}\begin{bmatrix}d^{m,n} & d^{m,n} & d^{k,l} \\{e^{j\;\alpha}d^{m,n}} & {{- e^{j\;\alpha}}d^{m,n}} & {e^{j\;\beta}d^{k,l}}\end{bmatrix}$ ${\frac{1}{\sqrt{12}}\begin{bmatrix}d^{m,n} & d^{k,l} & d^{k,l} \\{e^{j\;\alpha}d^{m,n}} & {e^{j\;\beta}d^{k,l}} & {{- e^{j\;\beta}}d^{k,l}}\end{bmatrix}},\left\{ {m,n} \right\},{\left\{ {k,l} \right\} = 0},\ldots\mspace{14mu},{{N_{p}/2} - 1},{m \neq n},{k \neq l},{\left\{ {\alpha,\beta} \right\} = 0},{\pi/2}$wherein d^(m,n) is a vector of length N_(p)/2.
 17. The UE of claim 4,the UE to further: calculate the CSI of the transmission channel usingthe codebook, wherein the codebook for rank 4 CSI reporting contains atleast one element from the following set:${\frac{1}{\sqrt{16}}\begin{bmatrix}d^{m,n} & d^{m,n} & d^{k,l} & d^{k,l} \\{e^{j\;\alpha}d^{m,n}} & {{- e^{j\;\alpha}}d^{m,n}} & {e^{j\;\beta}d^{k,l}} & {{- e^{j\;\beta}}d^{k,l}}\end{bmatrix}},\left\{ {m,n} \right\},{\left\{ {k,l} \right\} = 0},\ldots\mspace{14mu},{{N_{p}/2} - 1},{m \neq n},{k \neq l},{\left\{ {\alpha,\beta} \right\} = 0},{\pi/2}$wherein d^(m,n) is a vector of length N_(p)/2.
 18. The UE of claim 14,wherein in vector d^(m,n) a value of “1” occupies an m^(th) position ofthe vector, a value of “−1” occupies an n^(th) position of the vector,where m is unequal to n, and a value of “0” occupies other positions ofthe vector.
 19. The UE of claim 14, wherein in vector d^(m,n): a valueof “1” occupies the m^(th) and n^(th) positions of the vector, where mis unequal to n, and a value of “0” occupies the other positions of thevector; or a value of “1” occupies the m^(th) position, a value of “−1”occupies the n^(th) positions of the vector, and a value of “0” occupiesother positions of the vector.
 20. The UE of claim 14, wherein in vectord^(m,n) a non-integer value occupies the m^(th) and n^(th) positions,where m is unequal to n, and a value of “0” occupies the otherpositions.
 21. The UE of claim 14, wherein the vector d^(m,n) of lengthN_(p)/2 includes non-integer values in the n^(th) and m^(th) elements(noted as d^(i)), where m is unequal to n, as follows:$d^{i} = \left\{ \begin{matrix}{d_{m},} & {i = m} \\{d_{n},} & {i = n} \\{0,} & {otherwise}\end{matrix} \right.$ wherein m is not equal to n.
 22. The UE of claim1, wherein the codebook follows an uplink codebook defined in TS 36.211v. 11.4.0, section 5.3.3A.2 to support uplink transmissions.
 23. Anapparatus to operate in a cellular′ network, the apparatus comprising: aplurality of antennas to receive and transmit signals; a codebookcomprising a matrix, the matrix comprising non-constant moduluselements, wherein a column of the matrix corresponds to amultiple-input-multiple-output (MIMO) layer and a row of the matrixcorresponds to an antenna port and wherein a precoding vector among aplurality of vectors of the codebook contains at least two non-zeroelements; and baseband circuitry is configured to: receive a radio framecomprising a channel state information reference signal (CSI-RS);calculate channel state information (CSI) using both the CSI-RS and thecodebook; and report the CSI to the cellular network.
 24. The apparatusof claim 23, wherein the codebook comprises: a first codebook comprisingprecoding matrices for rank 1, rank 2, rank 3, and rank 4, the firstcodebook comprising first selection vectors of length N_(p)/2, whereN_(p) is a total number of CSI-RS antenna ports, wherein a value of “1”occupies an m^(th) position and a value of “0” occupies other positionsof the first selection vectors; and a second codebook also comprisingprecoding matrices for rank 1, rank 2, rank 3, and rank 4, the secondcodebook comprising second selection vectors of length N_(p)/2, wherein:a value of “1” occupies n^(th) and m^(th) positions of the secondselection vectors, where m is unequal to n, and a value of “0” occupiesthe other positions of the second selection vectors; or a value of “1”occupies the m^(th) position, a value of “−1” occupies the n^(th)positions of the second selection vectors, and a value of “0” occupiesother positions of the second selection vectors.